This invention relates to apparatus for treating sewage sludge in a hyperbaric vessel in which the sludge is oxygenated by injecting an oxygen-rich gas into the sewage sludge and then dispersing the mixture of sludge and oxygen-rich gas into the upper portion of a hyperbaric vessel for further interaction with an oxygen-rich atmosphere.
Traditionally, sewage, and specifically sludge, has been difficult to treat because it is, almost by definition, extremely variable in composition. In addition to human liquid and solid organic waste, the sludge to be treated in accordance with the present invention may include industrial and commercial sludge which is susceptible to aerobic treatment. In general, the present invention provides a means and process for highly efficient interaction of sludge particles with an oxygen-rich gas, in the form of O.sub.2 gas (oxygen) and/or O.sub.3 gas (ozone).
The present invention is intended primarily for treatment of activated sludge, namely, waste from domestic, commercial and industrial sources which create a biologically degradable material. A batch of pH adjusted waste to be treated is mixed with an oxygen-rich gas, the mixture is divided into small droplets and the droplets are dispersed within a pressure vessel where they are oxygenated by being exposed to an oxygen-rich gas for a substantial period of time. The Biological Oxygen Demand (BOD) and the Chemical Oxygen Demand (COD) of the waste are substantially saturated and satisfied. The addition of ozone produces an almost complete destruction and elimination of coliform, fecal coliform, salmonella and other harmful bacteria from the batch of sludge being treated. Although the coliform and fecal coliform bacteria are not in themselves particularly harmful, when they are present, it is recognized that other harmful bacteria are present. Thus, when the coliform and fecal coliform bacteria are destroyed, it is an indication that the other harmful bacteria, which are more difficult to detect, are also destroyed.
The present invention is intended to be used in a large scale sewage treatment system for treating activated sludge which is generally too thick to be treated efficiently on a large scale basis by presently existing commercial equipment. The present invention can be incorporated with presently existing wastewater treatment plants. Most existing wastewater treatment plants are capable of producing sludge with a solid content of about one and one-half percent by weight. The present invention has been designed to treat sludge having a solid content of greater than two percent to about four percent by weight, more preferably from about three percent to about three and one-half percent.
Various prior art references have dealt with treating sewage or water by aeration, oxidation or ozonation, as well as with dispersement in hyperbaric vessels. None, however, has all of the features of the present invention.
One of the co-inventors of the present invention developed a series of improved sludge treatment systems as illustrated, described and claimed in U.S. Pat. Nos. 4,487,699, 4,582,612, 4,659,464 and 4,695,388 of Charles A. Long, Jr., the disclosures of which are hereby incorporated by reference. While the sludge treating systems, processes and apparatus disclosed in the foregoing Long, Jr. patents enhanced the treatment of sludge compared to the systems, processes and apparatus previously known for that purpose, the present inventors devised a way to still further enhance the treatment of sewage sludge to reduce the bacteria, as well as viruses, parasites and other pathogens in the treated sludge to below currently detectable levels in a relatively short time and in an efficient manner.
Another aspect of the present invention relates to the further handling of the treated sludge product which will be less objectionable to the public. The sludge product treated according to the present invention has substantially reduced pathogens than prior art sludges. Moreover, the treated sludges used to make a sludge cake which can be hauled to a landfill, or otherwise used or processed into a product which does not produce such a foul odor that the such products would be objectionable to the public.